The present invention relates generally to a rodless cylinder used to operate various machines, and more particularly to a rodless cylinder with a speed control mechanism that enables a piston to be smoothly accelerated at the initial end of the stroke and smoothly decelerated at the terminus of the stroke.
One typical example of such a rodless cylinder is disclosed in JP-A 63-96305. In this rodless cylinder, a piston is slidably inserted in a cylinder tube and a head cover is fixed at either end of the cylinder tube. The piston is provided with a connector which projects outwardly from a slit in the cylinder tube and which is fixedly provided with a table member. End blocks at both ends of the piston are provided with concave portions that are open at said both ends. Within the head cover located at the position opposite to each concave portion there is a columnar form of convex portion (cushion ring) that is fitted into the concave portion. The apex part of the convex portion is provided with a hole in communication with an air feed port, in which hole a check valve is located. In the apex of the concave portion there is a nozzle hole for bypassing the check valve. The head cover is provided with a narrow bypass which is located between the air feed port and the inner portion of the tube that is adjacent to the outer surface thereof, and which is provided with a needle valve.
In the conventional rodless cylinder mentioned above, when the piston is moved to the terminal region of the stroke where the concave portion of the piston is engaged with the convex portion of the head cover, the discharge of air from the check valve is stopped, so that the space surrounding the concave portion is gradually depressurized through the needle valve. By the table member coupled to the piston, load kinetic energy and driving force energy, the air in the exhaust chamber is compressed and pressurized, so that the piston can be decelerated at a given rate. On the other hand, when the piston is positioned at the initial end of the stroke, the amount of the inflowing air is reduced by the needle valve and nozzle, so that the piston can be accelerated at a given rate. However, since the convex portion (cushion ring) is made integral with the head cover, it is impossible to change the time and magnitude of acceleration and deceleration of the piston.
In view of the problem mentioned above, a primary object of the invention is to change the position of the cushion ring and hence the flow rate of air passing around the cushion ring, thereby regulating the time and magnitude of acceleration and deceleration of the piston.